Process for electrically interconnecting chips with substrates employing gold alloy bumps and magnetic materials therein

Abstract

Gold alloy bumps are built up upon conductive pads formed upon electronic chips. The bumps are thereafter aligned with conductive portions of a generally larger substrate to which the chips are to be electrically connected. The bumps are produced by either vacuum evaporating or plating metallic layers over the conductive chip pad areas wherein certain layers within the bumps are formed of magnetic metals such as cobalt or nickel cobalt alloys. Metallic layers of gold and alloying metal are evaporated or plated over the deposited magnetic metals to complete the formation of the bumps. The chips are thereafter subjected to a sufficient amount of heat to cause the bumps to flow, thereby to form a reliable electrical connection between the chips and the substrate. The magnetic materials formed within the bumps result in ease of transporting and manipulating the chips for further processing by means of magnetic plates or other pickup devices. The flowing of the bumps renders the electrical interconnections between the chips and substrate self-aligning since the molten alloy will be attracted to and bond to the adjacent conductive substrate pads rather than the non-metallic portions immediately adjacent the pads. Reliable interconnections are made to multiple substrate pads by virtue of the ductile metallurgy of the bump material.

What is claimed is: 
     
       1. A method for connecting a first electrical circuit means to a second electrical circuit means wherein said first electrical circuit means has a plurality of bumps which upon being heated partially melt to form electrical contacts with conductive portions of said second electrical circuit means without short circuiting, said method comprising the steps of: a. forming solder bumps upon said first set of conductive areas of said first electrical device, said bumps having a hard metallic inner core and having an outer portion of soft solder metal at least partially surrounding said hard metallic inner core, the volume of said inner core of hard metal being approximately 25% to 50% of the total volume of the bump to produce controlled bump collapse for preventing said short circuiting during the carrying out of step (c);   b. aligning said solder bumps with said conductive portions of said second electrical circuit means; and   c. heating said solder bumps to a sufficient extent to cause the soft outer metallic portion of said solder bumps to flow and produce an electrical connection between said first electrical circuit means and said second electrical circuit means.   
     
     
       2. The method of claim 1 wherein said hard metallic inner core comprises a magnetizable material, and further including the steps of magnetizing said magnetizable material before step (c), thereby to facilitate the manipulation of said bumps by means of magnetic pick-up devices. 
     
     
       3. The method of claim 2 wherein said hard metallic inner core comprises an alloy containing iron, nickel, and cobalt. 
     
     
       4. The method of claim 3 wherein said hard metallic inner core comprises an alloy of about 58% iron, 27% nickel, and 15% cobalt, to provide particularly high saturation induction. 
     
     
       5. The method of claim 1 wherein said outer portion comprises a gold alloy solder composition, and said hard metallic inner core extends from said first electrical circuit means toward said second electrical circuit means. 
     
     
       6. The method of claim 5 wherein said solder composition consists of gold, lead, and silver. 
     
     
       7. The method of claim 6 wherein said solder composition consists of about 16% gold, 4% silver, and 80% lead. 
     
     
       8. The method of claim 1 wherein said outer portion consists of a solder composition of lead, indium, and silver. 
     
     
       9. The method of claim 8 wherein said solder composition is almost 50% lead and almost 50% indium with a minor percentage of silver. 
     
     
       10. The method of claim 1 wherein said outer portion comprises a gold alloy solder composition, and said hard metallic inner core extends from said first electrical circuit means toward said second electrical circuit means. 
     
     
       11. The method of claim 5 wherein said solder composition consists of gold, lead, and silver. 
     
     
       12. The method of claim 6 wherein said solder composition consists of about 16% gold, 4% silver, and 80% lead. 
     
     
       13. The method of claim 1 wherein said outer portion consists of a solder composition of lead, indium, and silver. 
     
     
       14. The method of claim 13 wherein said solder composition is almost 50% lead and almost 50% indium with a minor percentage of silver. 
     
     
       15. The method of claim 1 wherein the volume of said inner core of hard metal is about 50% of the total volume of the bump.